Visual perception is mediated by complex interactions amongst neurons in the retina, visual cortex, and subcortical brain structures. The importance of vision to humans and other primates is reflected in the enormous percentage of cerebral cortex devoted to processing visual information. Thus, deficits in visual processing are particularly debilitating and arise from abnormalities not only in the eye, but also in cortical circuitry. For example, strabismus or amblyopia during childhood can have long-lasting effects on the cortical circuits that process visual information. There is also evidence that some forms of dyslexia result from central visual system abnormalities. The function of the nervous system is dependent on complex interactions between networks of neurons composed of multiple neuron types. The proposed studies are aimed at revealing the organization and function of mouse visual cortical areas. Such studies will provide a crucial framework for detailed functional investigations of visual cortical circuits using novel genetic, viral and transgenic approaches tha have been developed at the cutting edge of neuroscience over the last several years. Because these tools are most powerful in mice and many basic principles of the organization and function of cortical circuits are conserved from mice to humans, development of the mouse system represents in extremely important direction for future studies. The 3 aims will reveal: the visual receptive field properties of neurons in each of nine mouse extrastriate visual areas; the functional properties of V1 neurons that project to extrastriate visual areas; and the connections between extrastriate visual areas and to subcortical structures.